Electrically-Switchable Angle-Dependent Plasmonic Coloration

Optical encryption using plasmonics is a superior concept for security as it offers fade-free rich colorations with viewing-angle and/or polarization dependency.[1] However, such plasmonic coloration typically not only necessitates complex nano-lithographic patterning for multilayered plasmonic systems with their precise nanoscale dimension, but also remains in the production of static image planes.<br/>We here present a ‘lithography-free’ method to fabricate wafer-scale multi-layered ‘active’ plasmonic metasurfaces, which show angle-dependent as well as electrically switchable coloration across the whole visible spectra. The physical vacuum growth with substrate cooling allows us to grow a wafer-scale array of dense plasmonic nanoaggregates on a metallic mirror coated with a conductive polymer layer (here polyaniline). Such nanoparticle-on-mirror constructs filled with polyaniline intrinsically possess two dominant gap plasmonic modes, i.e. (i) in-plane coupling between densely-positioned nanoparticles and (ii) out-of-plane coupling between the nanoparticles and the mirror underneath. These two coupling modes can be excited selectively depending on an incident angle of the light and thus reveal a vivid color transition. More crucially, such colors can now be further electrically tunable in response to an external voltage applied (&lt; 1V), thanks to the change in the redox states of the polyaniline within the nanojuctions and thus associated refractive indices.[2] With the combinatorial control in the light angle and the electrical input, the single plasmonic metasurface gives rise to rich colorations across the whole visible spectra, potentially useful for ‘active’ optical information storage and encryption.<br/>In this presentation, the structural design, numerical simulation, fabrication method, optical feature and analysis of the electrically switchable plasmonic metasurfaces will be discussed.<br/><br/>[1] J. Park et. al, Adv. Mat. 2021, <b>33</b>, 2007831<br/>[2] J. Peng et. al, Sci. Adv. 2019, <b>12</b>, eeaw2205